Several operations may be employed to facilitate oil and gas exploration and production operations. One example is a hydraulic fracturing operation, during which hydraulic fracturing fluid, or slurry, is pumped to a wellhead for the purpose of propagating fractures in a subterranean formation in which a wellbore extends, the wellhead being the surface termination of the wellbore. The hydraulic fracturing fluid or slurry is used to fracture the subterranean formation. During and after the hydraulic fracturing operation, the fluid used in the operation flows back up to, and out of, the wellhead. This wellbore fluid flow may be referred to as “frac flow-back,” and the fluid itself may be referred to as “flow-back.” The flow-back may include the hydraulic fracturing fluid or slurry pumped to the wellhead, as well as fluids and other materials from the fractured formation. Another example of an operation employed to facilitate oil and gas exploration and production operation is a well testing operation, during which fluid is pumped to the wellhead and into the wellbore to test the formation; this fluid also flows back up to, and out of, the wellhead. During operations involving wellbore fluid flow out of the wellhead, such as hydraulic fracturing or well testing operations, the wellbore fluid flow out of the wellbore must be controlled to maintain the integrity of the wellbore and, in many cases, maximize production from the wellbore. For example, if the wellbore fluid flow is too fast (i.e., the wellbore fluid volumetric flow rate or velocity is too high), the wellbore may collapse, decreasing production. Conversely, if the wellbore fluid flow is too slow (i.e., the wellbore fluid volumetric flow rate or velocity is too low), the wellbore may clog, also decreasing production. Further, during operations involving wellbore fluid flow out of the wellhead, such as hydraulic fracturing or well testing operations, the wellbore fluid flow out of the wellbore must be monitored and/or controlled to prevent, or at least minimize the risk of, erosion, washout or rupture of valves, flow lines, flow iron, etc. through which the wellbore fluid flows. Still further, during operations involving wellbore fluid flow out of the wellhead, such as hydraulic fracturing or well testing operations, the wellbore fluid flow out of the wellbore must be monitored and/or controlled to monitor the composition of vent gas (i.e., the percentage of the vent gas that is production gas (e.g., methane), the percentage of the vent gas that is gas used in a hydraulic fracturing operation (e.g., carbon dioxide), other percentage(s) of the vent gas, etc.). Therefore, what is needed is a system, method, kit, apparatus, or assembly that addresses one or more of these issues, and/or other issue(s).